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Field.Required Property (DAO)

  • 아티클

Sets or returns a value that indicates whether a Field object requires a non-Null value.

Syntax

expression .Required

expression A variable that represents a Field object.

Remarks

For a Field not yet appended to the Fields collection, this property is read/write.

The availability of the Required property depends on the object that contains the Fields collection, as shown in the following table.

If the Fields collection belongs to a

Then Required is

Index object

Not supported

QueryDef object

Read-only

Recordset object

Read-only

Relation object

Not supported

TableDef object

Read/write

You can use the Required property along with the AllowZeroLength, ValidateOnSet, or ValidationRule property to determine the validity of the Value property setting for that Field object. If the Required property is set to False, the field can contain null values as well as values that meet the conditions specified by the AllowZeroLength and ValidationRule property settings.

Note

When you can set this property for either an Index object or a Field object, set it for the Field object. The validity of the property setting for a Field object is checked before that of an Index object.

Example

This example uses the Required property to report which fields in three different tables must contain data in order for a new record to be added. The RequiredOutput procedure is required for this procedure to run.

Sub RequiredX() 
 
 Dim dbsNorthwind As Database 
 Dim tdfloop As TableDef 
 
 Set dbsNorthwind = OpenDatabase("Northwind.mdb") 
 
 With dbsNorthwind 
 ' Show which fields are required in the Fields 
 ' collections of three different TableDef objects. 
 RequiredOutput .TableDefs("Categories") 
 RequiredOutput .TableDefs("Customers") 
 RequiredOutput .TableDefs("Employees") 
 .Close 
 End With 
 
End Sub 
 
Sub RequiredOutput(tdfTemp As TableDef) 
 
 Dim fldLoop As Field 
 
 ' Enumerate Fields collection of the specified TableDef 
 ' and show the Required property. 
 Debug.Print "Fields in " & tdfTemp.Name & ":" 
 For Each fldLoop In tdfTemp.Fields 
 Debug.Print , fldLoop.Name & ", Required = " & _ 
 fldLoop.Required 
 Next fldLoop 
 
End Sub